This invention relates generally to seat belt assemblies of vehicles, particularly motor vehicles, that are designed to minimize the risk of bodily harm in an accident or emergency. More specifically, the invention deals with an emergency locking seat belt retractor of the type responsive to vehicle acceleration. It should be understood that the term "acceleration" is herein used generically, to mean both "positive" and "negative" accelerations as well as a sudden change in direction of movement of the vehicle.
Emergency locking retractors have been known and used in conjunction with vehicle seat belt assemblies. A retractor of this class usually includes a drum or reel on which there is wound a storage portion of the seat belt and which is spring biased to rotate in the belt winding direction. Normally, therefore, the occupant of the vehicle seat can wear the belt under tension while being relatively free to move away from or back to his seat. The retractor in question also includes a locking mechanism which is actuated automatically, as in the event of collision, rollover, or any abrupt stopping of the vehicle, to lock the drum against rotation in the belt unwinding direction.
In the known mechanical emergency locking retractor of the type responsive to vehicle acceleration, the force required to actuate the locking mechanism has been derived directly from a displaceable inertial element constituting the principal part of acceleration sensing means. A problem accompanying such prior art arrangement is that the locking mechanism becomes completely inoperative in the event that the inertial element is hurled away or otherwise becomes lost from its housing or support structure as a result of, for example, the collision of the vehicle. This disadvantage is all the more serious because the acceleration sensing means with its displaceable inertial element is more susceptible to the effects of shocks than the other part or component of the vehicle.